Glutamate, the major amino-acid transmitter in the mammalian central nervous system (CNS), mediates excitatory synaptic neurotransmission through the activation of ionotropic glutamate receptors receptor-channels (iGluRs, namely NMDA, AMPA and kainate) and metabotropic glutamate receptors (mGluRs). iGluRs are responsible for fast excitatory transmission (Nakanishi S. et al., (1998) Brain Res. Rev., 26:230-235) while mGluRs have a more modulatory role that contributes to the fine-tuning of synaptic efficacy. Glutamate is associated with numerous physiological functions such as long-term potentiation (LTP), a process believed to underlie learning and memory but also cardiovascular regulation, sensory perception, and the development of synaptic plasticity. In addition, glutamate plays an important role in the patho-physiology of different neurological and psychiatric diseases, especially when an imbalance in glutamatergic neurotransmission occurs.
The mGluRs are seven-transmembrane G protein-coupled receptors. The eight members of the family are classified into three groups (Groups I, II & III) according to their sequence homology and pharmacological properties (Schoepp D. D. et al. (1999) Neuropharmacology, 38:1431-1476). Activation of mGluRs leads to a large variety of intracellular responses and activation of different transductional cascades. Among mGluR members, the mGluR5 subtype is of high interest for counterbalancing the deficit or excesses of neurotransmission in neuropsychatric diseases. mGluR5 belongs to Group I and its activation initiates cellular responses through G-protein mediated mechanisms. mGluR5 is coupled to phospholipase C and stimulates phosphoinositide hydrolysis and intracellular calcium mobilization.
mGluR5 proteins have been demonstrated to be localized in post-synaptic elements adjacent to the post-synaptic density (Lujan R. et al. (1996) Eur. J. Neurosci. 8:1488-500; Lujan R. et al. (1997) J. Chem. Neuroanat., 13:219-41) and are also detected in the pre-synaptic elements (Romano C. et al. (1995) J. Comp. Neurol. 355:455-69). MGluR5 receptors can therefore modify the post-synaptic responses to neurotransmitter or regulate neurotransmitter release.
In the CNS, mGluR5 receptors are abundant mainly throughout cortex, hippocampus, caudate-putamen and nucleus accumbens. As these brain areas have been shown to be involved in emotion, motivational processes and in numerous aspects of cognitive function, mGluR5 modulators are predicted to be of therapeutic interest.
A variety of clinical indications have been suggested to be targets for the development of subtype selective mGluR modulators. These include epilepsy, neuropathic and inflammatory pain, numerous psychiatric disorders (eg anxiety and schizophrenia), movement disorders (eg Parkinson disease), neuroprotection (stroke and head injury), migraine and addiction/drug dependency (for reviews, see Brauner-Osborne H. et al. (2000) J. Med. Chem. 43:2609-45; Bordi F. and Ugolini A. (1999) Prog. Neurobiol. 59:55-79; Spooren W. et al. (2003) Behay. Pharmacol. 14:257-77).
mGluR5 receptor is considered as a potential drug target for the treatment of psychiatric and neurological disorders Anxiety Disorders, Attentional disorders, Eating Disorders, Mood Disorders, Psychotic Disorders, Cognitive Disorders, Personality Disorders and Substance of Abuse related disorders
Other research supports a role of mGluR5 modulation in the treatment of Fragile X syndrome (Laura N. Antar et al. The Journal of Neuroscience, Mar. 17, 2004, 24-11, 2648-2655, Weiler I. J., Proc. Natl. Acad. Sci. USA, 1997, 94, 5395-5400), Obesity and Gastro-Esophageal Reflux Disease (Blackshaw L. A. et al., presentation at the conference Neurogastroentorology & Morality, Madison, Wis., 14 Nov. 2001).
International Patent Publications WO03/104206, GB2124227, WO03/050087 and WO03/013247 describe 3-phenoxyprop-1-ynyl and 3-pyridinoxyprop-1-ynyl, having herbicidal properties. In U.S. Pat. No. 6,166,060, 4-(5-phenylpent-1-ynyl)-1H-imidazole is described as an H3 histamine antagonist.
International patent publications WO99/02497, WO01/16121 and WO02/46166 describe heteroaryl ethynyl compounds and their use as metabotropic glutamate receptor antagonists. International patent publications WO2005/044265, WO2005/044266 and WO2005/044267 disclose a class of 3-(pyridin-2-yl)prop-2-ynyl derivatives as being useful in GERD indication.
Compounds of general formula I can show potent activity and selectivity on mGluR5 receptor. The compounds of the invention can demonstrate advantageous properties over compounds of the prior art. Improvements have been observed in one or more of the following characteristics of the compounds of the invention: the potency on the target, the selectivity for the target, the solubility, the bioavailability, the brain penetration, and the activity in behavioural models of psychiatric and neurological disorders.
The present invention relates to a method of treating or preventing a condition in a mammal, including a human, the treatment or prevention of which is affected or facilitated by the neuromodulatory effect of mGluR5 modulators.